Round reinforcing bars are generally bundled in lots weighing about 5 tons, and have a length of 12 to 18 meters. Obviously there is a relatively broad range of round bars with different cross sections adapted for use with different structures to be built.
The shearing of round reinforcing bars can be organized in two principal ways, as a function of the quantity of steel to be sheared every day, which can be a function of the size of the company carrying out the work.
The first method is to prepare all the elements in one order before going on to those in the next order. Each type of bar is stored in a bin and the shear is mounted so that it can move in front of the bins and be brought up to those containing various types of bars to be sheared one at a time. When the shear has passed all the bins, the order is finished and ready for shipping.
Another method is to group a certain number of orders together, such as all the orders for one day. Within this group of orders, or manufacturing program, all the bars of a given diameter are combined so that the same type of product can be worked on for a relatively long period of time.
Generally, when several orders are combined, each batch of the same type of bar may total 5 tons. In this case, it is more efficient to move the 5 ton batch up to the shear point than to move the shear relative to the batch of bars.
However, this faster method has the disadvantage of making it necessary to sort the bar diameters after shearing, in order to fill the original orders.
The various operations involved in cutting by this second method are the following:
sorting the bars into 5-ton batches of the same diameter to feed them one by one;
grouping together a number of bars to be cut simultaneously;
moving these bars up to the shear;
measuring the length to be cut;
shearing;
taking cut bars away from the shear;
removal of the cut bars;
storing these bars in appropriate bins.
Traditional shearing systems using this method thrust the bars mechanically or manually against stops at a distance from the shear corresponding to the length to be cut.
Since commercial bars are 12 to 18 meters long, to avoid waste, a long length and a short length are frequently cut from the same bar to achieve optimum utilization. Thus, the stop must be adjusted over a long distance each time the bar is cut, which is time-consuming, or several stops must be available, involving complicated machinery and high cost.
In addition, most machines of this type move the bars at high speed over metal rollers. However, in general the bars are not smooth but serrated or ribbed so that the noise caused by their movement is extremely loud, on the order of 110 decibels.